CiteULike: Author Bertrand

Simple points, topological numbers and geodesic neighborhoods in cubic grids

Giles Bertrand — 2008-07-23T06:19:12-00:00

Pattern Recognition Letters, Vol. 15, No. 10. (October 1994), pp. 1003-1011.

We introduce the notion of geodesic neighborhood in order to define some topological numbers associated with a point in a three-dimensional cubic grid. For 6, 26 and 6, 18 connectivities, these numbers lead to a characterization of simple points which consists in only two local conditions.

Open software for biologists: from famine to feast

Dawn Field — 2006-07-16T22:10:39-00:00

Nature Biotechnology, Vol. 24, No. 7., pp. 801-803.

The transcriptional cycle of HIV-1 in real-time and live cells.

S Boireau — 2007-11-12T12:32:05-00:00

J Cell Biol, Vol. 179, No. 2. (22 October 2007), pp. 291-304.

RNA polymerase II (RNAPII) is a fundamental enzyme, but few studies have analyzed its activity in living cells. Using human immunodeficiency virus (HIV) type 1 reporters, we study real-time messenger RNA (mRNA) biogenesis by photobleaching nascent RNAs and RNAPII at specific transcription sites. Through modeling, the use of mutant polymerases, drugs, and quantitative in situ hybridization, we investigate the kinetics of the HIV-1 transcription cycle. Initiation appears efficient because most polymerases demonstrate stable gene association. We calculate an elongation rate of approximately 1.9 kb/min, and, surprisingly, polymerases remain at transcription sites 2.5 min longer than nascent RNAs. With a total polymerase residency time estimated at 333 s, 114 are assigned to elongation, and 63 are assigned to 3'-end processing and/or transcript release. However, mRNAs were released seconds after polyadenylation onset, and analysis of polymerase density by chromatin immunoprecipitation suggests that they pause or lose processivity after passing the polyA site. The strengths and limitations of this kinetic approach to analyze mRNA biogenesis in living cells are discussed.

L'analyse de la matière

Bertrand Russell — 2008-07-02T11:04:44-00:00

(1965)

Shear Thickening of Cornstarch Suspensions as a Reentrant Jamming Transition

Abdoulaye Fall — 2008-03-18T01:32:20-00:00

Physical Review Letters, Vol. 100, No. 1. (2008)

We study the rheology of cornstarch suspensions, a non-Brownian particle system that exhibits shear thickening. From magnetic resonance imaging velocimetry and classical rheology it follows that as a function of the applied stress the suspension is first solid (yield stress), then liquid, and then solid again when it shear thickens. For the onset of thickening we find that the smaller the gap of the shear cell, the lower the shear rate at which thickening occurs. Shear thickening can then be interpreted as the consequence of dilatancy: the system under flow wants to dilate but instead undergoes a jamming transition because it is confined, as confirmed by measurement of the dilation of the suspension as a function of the shear rate.

ATP as a Putative Sensory Mediator: Activation of Intrinsic Sensory Neurons of the Myenteric Plexus via P2X Receptors

Paul Bertrand — 2008-06-30T00:26:50-00:00

J. Neurosci., Vol. 22, No. 12. (15 June 2002), pp. 4767-4775.

The mucosal terminals of sensory neurons intrinsic to the wall of the intestine are sensitive to the chemical environment within the lumen. Lumenal stimuli probably release sensory mediators from the mucosal epithelium, which then activate the nerve terminals indirectly. Here, we tested the idea that ATP activates intrinsic sensory nerve terminals in a way consistent with its being a sensory mediator.We made intracellular recordings from intrinsic sensory neurons located in the myenteric plexus [identified as AH neurons, which are neurons with a long-lasting afterhyperpolarization following the action potential (AP)], located within 1 mm of intact mucosa. Focal electrical stimulation of the mucosa was used to locate and map regions innervated by each neuron. Application of ATP (1-2 mM in the pressure pipette) to these regions elicited trains of APs that originated at the sensory terminals. ATP-[gamma]-S produced a similar response, but [alpha],[beta]-methylene ATP and 2-methylthio-ATP were only weakly active. The P2 receptor antagonist pyridoxalphosphate-6-azophenyl-2',5'-disulphonic acid (PPADS) (60 microM in the bath) abolished the APs evoked by ATP and ATP-[gamma]-S but spared similar responses evoked by 5-hydroxytryptamine (5-HT). Another P2 receptor antagonist suramin (100 microM in the bath) did not significantly change the number of APs evoked by ATP. Either ATP or [alpha],[beta]-methylene ATP desensitized the ATP-evoked APs; 50% recovery occurred after ~5 sec. The number of APs evoked by ATP was reduced, but not abolished, by the selective 5-HT3 receptor antagonist granisetron (1 microM in the bath).ATP was applied to the cell bodies of sensory neurons to investigate whether the cell bodies express the same P2X receptor as the terminals. ATP evoked a fast depolarization associated with a reduction in input resistance and a reversal potential of [-]11 mV. This depolarization was potentiated by suramin and blocked by PPADS.We conclude that activation of an atypical excitatory P2X receptor by ATP triggers AP generation in the mucosal processes of the sensory neurons; endogenous 5-HT release may also contribute to activation of the nerve terminals. A similar P2X receptor exists on the cell body of the sensory neuron. Together, these data are consistent with a role for ATP as a sensory mediator in gastrointestinal chemosensory transduction. 20026350

Waves of agitation inside anchovy schools observed with multibeam sonar: a way to transmit information in response to predation

Francois Gerlotto — 2008-06-27T14:37:07-00:00

ICES J. Mar. Sci., Vol. 63, No. 8. (1 January 2006), pp. 1405-1417.

Most pelagic fish live in schools. To allow fast reactions, for instance to predator attacks, these collective structures require behavioural mechanisms authorizing fast, coordinated movements. Considering the large number of individuals constituting a school of small pelagic fish, a crucial premise to coordinated movements and school reorganization is an ability to transfer quickly and efficiently information across the whole collective structure. We observed anchovy school movements and reactions to sea-lion attacks while the ship was drifting in Peruvian waters. The main process of information transfer we could observe was that of waves of agitation crossing large anchovy schools. The average speed of these waves (7.45 m s-1) was much greater than the average 0.3 m s-1 school speeds measured during this experiment. The internal organization of each school modified dramatically after the waves of agitation had crossed them. Changes in school external morphology and internal structure were described and measured using geostatistics. Our results show that information transfer is a crucial process for the cohesion and plasticity of schools. As such, it allows efficient reactions of schools of pelagic fish to variations in their immediate environment in general, and to predation in particular. 10.1016/j.icesjms.2006.04.023

Mechanism of Calcite Crystal Growth Inhibition by the N-terminal Undecapeptide of Lithostathine

Vincent Gerbaud — 2008-02-19T02:58:48-00:00

J. Biol. Chem., Vol. 275, No. 2. (14 January 2000), pp. 1057-1064.

Pancreatic juice is supersaturated with calcium carbonate. Calcite crystals therefore may occur, obstruct pancreatic ducts, and finally cause a lithiasis. Human lithostathine, a protein synthesized by the pancreas, inhibits the growth of calcite crystals by inducing a habit modification: the rhombohedral 10 [1]4 usual habit is transformed into a needle-like habit through the 11 [IMG]img001.gif" ALT="">0 crystal form. A similar observation was made with the N-terminal undecapeptide (pE1R11) of lithostathine. We therefore aimed at discovering how peptides inhibit calcium salt crystal growth. We solved the complete x-ray structure of lithostathine, including the flexible N-terminal domain, at 1.3 A. Docking studies of pE1R11 with the (10 [1]4) and (11 [IMG]img001.gif" ALT="">0) faces through molecular dynamics simulation resulted in three successive steps. First, the undecapeptide progressively unfolded as it approached the calcite surface. Second, mobile lateral chains of amino acids made hydrogen bonds with the calcite surface. Last, electrostatic bonds between calcium ions and peptide bonds stabilized and anchored pE1R11 on the crystal surface. pE1R11-calcite interaction was stronger with the (11 [IMG]img001.gif" ALT="">0) face than with the (10 [1]4) face, confirming earlier experimental observations. Energy contributions showed that the peptide backbone governed the binding more than did the lateral chains. The ability of peptides to inhibit crystal growth is therefore essentially based on backbone flexibility. 10.1074/jbc.275.2.1057

Crystal structure of human lithostathine, the pancreatic inhibitor of stone formation.

JA Bertrand — 2008-06-25T12:06:42-00:00

The EMBO journal, Vol. 15, No. 11. (3 June 1996), pp. 2678-2684.

Human lithostathine (HLIT) is a pancreatic glycoprotein which inhibits the growth and nucleation of calcium carbonate crystals. The crystal structure of the monomeric 17 kDa HLIT, determined to a resolution of 1.55 angstroms, was refined to a crystallographic R-factor of 18.6%. Structural comparison with the carbohydrate-recognition domains of rat mannose-binding protein and E-selectin indicates that the C-terminal domain of HLIT shares a common architecture with the C-type lectins. Nevertheless, HLIT does not bind carbohydrate nor does it contain the characteristic calcium-binding sites of the C-type lectins. In consequence, HLIT represents the first structurally characterized member of this superfamily which is not a lectin. Analysis of the charge distribution and calculation of its dipole moment reveal that HLIT is a strongly polarized molecule. Eight acidic residues which are separated by regular 6 angstrom spacings form a unique and continuous patch on the molecular surface. This arrangement coincides with the distribution of calcium ions on certain planes of the calcium carbonate crystal; the dipole moment of HLIT may play a role in orienting the protein on the crystal surface prior to the more specific interactions of the acidic residues.

Adaptation increases the likelihood of diversification in an experimental bacterial lineage.

CC Spencer — 2008-06-24T12:13:34-00:00

Proceedings of the National Academy of Sciences of the United States of America, Vol. 105, No. 5. (5 February 2008), pp. 1585-1589.

Understanding the mechanisms and processes that generate biological diversity is a fundamental problem in evolution and ecology. In the past decade, the theory of evolutionary branching and adaptive diversification has provided new perspectives for understanding the evolution of diversity caused by ecological interactions. In models of adaptive diversification, the fitness landscapes change dynamically, so that the likelihood of diversification into different phenotypic clusters increases over time. In contrast, in models with static fitness landscapes, the likelihood of diversification decreases as populations climb fitness peaks, because crossing maladaptive fitness valleys becomes increasingly difficult. We used experimental evolution in bacteria to test how the likelihood of diversification changes over time in a bacterial lineage that has diversified in sympatry from a single ancestral strain. By analyzing the "fossil" record of this lineage, and restarting the lineage from different time points in the evolutionary past, we demonstrate that: (i) the lineage has initially undergone a phase of directional adaptation to the competitive environment, and (ii) during this phase, the likelihood of diversification increases significantly over time. These results suggest evolutionary branching caused by frequency-dependent competition as the main mechanism of diversification in our experimental populations.

Flow of Wet Granular Materials

N Huang — 2008-06-22T00:55:36-00:00

Physical Review Letters, Vol. 94, No. 2. (2005)

The transition from frictional to lubricated flows of a dense suspension of non-Brownian particles is studied. The pertinent parameter characterizing this transition is the Leighton number Le = , the ratio of lubrication to frictional forces. Le defines a critical shear rate below which no steady flow without localization exists. In the frictional regime the shear flow is localized. The lubricated regime is not simply viscous: the ratio of shear to normal stresses remains constant and the velocity profile has a universal form in both frictional and lubricated regimes. Finally, a discrepancy between local and global measurements of viscosity is identified, which suggests inhomogeneity of the material under flow.

Pseudomonas aeruginosa fimL regulates multiple virulence functions by intersecting with Vfr-modulated pathways

Cynthia Whitchurch — 2005-02-18T11:10:09-00:00

Molecular Microbiology, Vol. 55, No. 5. (March 2005), pp. 1357-1378.

Interactions between fish and fisher's spatial distribution and behaviour: an empirical study of the anchovy (Engraulis ringens) fishery of Peru

Sophie Bertrand — 2008-06-20T04:44:10-00:00

ICES J. Mar. Sci., Vol. 61, No. 7. (1 January 2004), pp. 1127-1136.

Fishing data provide, with wide spatio-temporal coverage, inexpensive information about exploited species, but a precondition for their interpretation is a good comprehension of fish and fisher spatial dynamics and interactions. In Peru, anchovy (Engraulis ringens) is exploited by an industrial fleet of about 800 purse-seiners operating all along the coast. Using simultaneous acoustic survey and commercial fishing data for the 1998-2001 time period, we present a preliminary, exploratory, and empirical approach to identify the nature of potential interactions between Peruvian anchovy and fisher behaviour. We show that (i) Peruvian anchovy exhibited a composite spatial strategy for the study period, i.e. a change in biomass was associated with both change in geographical extension and density; (ii) fishing behaviour significantly varied within and among vessels in terms of travel duration, searching duration, and number of fishing sets; and (iii) interactions between fish and fisher behaviours differed according to the spatial scale. At a fish stock scale (the scale of fishing ground selection for fishers), fishing was more efficient with low biomass and high spatial concentration (low stock range and high biomass); at a local fish spatial scale (the scale of searching for a school inside the fishing ground), fishing performance was favoured by high mean local abundances and low spatial concentration (the way fish is distributed inside its stock range); finally, at the school scale (the scale of the fishing set), both high abundance and high spatial concentration were favourable to fishing success. 10.1016/j.icesjms.2004.07.016

Levy trajectories of Peruvian purse-seiners as an indicator of the spatial distribution of anchovy (Engraulis ringens)

Sophie Bertrand — 2008-06-20T04:43:12-00:00

ICES J. Mar. Sci., Vol. 62, No. 3. (1 January 2005), pp. 477-482.

Analogous to other top predators foraging on patchy resources, the spatial behaviour of fishers provides information on the spatial organization of fish. Focusing on the Peruvian anchovy purse-seine fishery, vessel monitoring system data are used to describe fishing vessels' trajectories, and acoustic survey data to characterize anchovy spatial distribution. Vessel trajectories were analysed in terms of move-length distribution, whereas fish distribution was characterized by spatial extent, concentration, and fractal dimension. Fishers perform Levy flights that can be characterized by a single statistic (micro); micro is significantly correlated with the fractal dimension of fish distribution. It is argued that the Levy statistic is a good candidate for an ecosystem indicator that might contribute to real-time monitoring of ecosystems. 10.1016/j.icesjms.2004.12.002

A non-periodic 2D semi-Lagrangian Vlasov code for laser-plasma interaction on parallel computer

A Ghizzo — 2008-06-10T16:14:47-00:00

Journal of Computational Physics, Vol. 186, No. 1. (20 March 2003), pp. 47-69.

For the first time, a 2D electromagnetic and relativistic semi-Lagrangian Vlasov model for a multi-computer environment was developed to study the laser-plasma interaction in an open system. Numerical simulations are presented for situations relevant to the penetration of an ultra-intense laser pulse inside a moderately overdense plasma and the relativistic filamentation instability in the case of an underdense plasma. The Vlasov model revealed a rich variety of phenomena associated with the fast particle dynamics induced by the laser pulse as particle trapping, particle acceleration and relativistic self-induced transparency in overdense plasma. Attention was focused on the efficiency and stability properties on the numerical scheme and implementation facilities on massively parallel computers. Success of the semi-Lagrangian Vlasov model is enhanced by the good conservation of the continuity equation and stability of Maxwell system due to the fine description of the electron distribution function and particularly of the charge density and current density.

Instability of the time splitting scheme for the one-dimensional and relativistic Vlasov-Maxwell system

F Huot — 2008-06-10T16:01:43-00:00

Journal of Computational Physics, Vol. 185, No. 2. (1 March 2003), pp. 512-531.

The Time Splitting Scheme (TSS) has been examined within the context of the one-dimensional (1D) relativistic Vlasov-Maxwell model. In the strongly relativistic regime of the laser-plasma interaction, the TSS cannot be applied to solve the Vlasov equation. We propose a new semi-Lagrangian scheme based on a full 2D advection and study its advantages over the classical Splitting procedure. Details of the underlying integration of the Vlasov equation appear to be important in achieving accurate plasma simulations. Examples are given which are related to the relativistic modulational instability and the self-induced transparency of an ultra-intense electromagnetic pulse in the relativistic regime.

Oscillatory gamma-band (30-70 Hz) activity induced by a visual search task in humans.

C Tallon-Baudry — 2006-11-01T13:21:20-00:00

J Neurosci, Vol. 17, No. 2. (15 January 1997), pp. 722-734.

The coherent representation of an object in the visual system has been suggested to be achieved by the synchronization in the gamma-band (30-70 Hz) of a distributed neuronal assembly. Here we measure variations of high-frequency activity on the human scalp. The experiment is designed to allow the comparison of two different perceptions of the same picture. In the first condition, an apparently meaningless picture that contained a hidden Dalmatian, a neutral stimulus, and a target stimulus (twirled blobs) are presented. After the subject has been trained to perceive the hidden dog and its mirror image, the second part of the recordings is performed (condition 2). The same neutral stimulus is presented, intermixed with the picture of the dog and its mirror image (target stimulus). Early (95 msec) phase-locked (or stimulus-locked) gamma-band oscillations do not vary with stimulus type but can be subdivided into an anterior component (38 Hz) and a posterior component (35 Hz). Nonphase-locked gamma-band oscillations appear with a latency jitter around 280 msec after stimulus onset and disappear in averaged data. They increase in amplitude in response to both target stimuli. They also globally increase in the second condition compared with the first one. It is suggested that this gamma-band energy increase reflects both bottom-up (binding of elementary features) and top-down (search for the hidden dog) activation of the same neural assembly coding for the Dalmatian. The relationships between high- and low-frequency components of the response are discussed, and a possible functional role of each component is suggested.

Optical properties of deep glacial ice at the South Pole

M Ackermann — 2008-06-10T12:41:13-00:00

Journal of Geophysical Research, Vol. 111 (8 July 2006), D13203.

Climate of the last millennium: a sensitivity study

Cedric Bertrand — 2008-06-05T15:21:50-00:00

Tellus A, Vol. 54, No. 3. (2002), pp. 221-244.

Seventy-one sensitivity experiments have been performed using a two-dimensional sector-averaged global climate model to assess the potential impact of six different factors on the last millennium climate and in particular on the surface air temperature evolution. Both natural (i.e, solar and volcanism) and anthropogenically-induced (i.e. deforestation, additional greenhouse gases, and tropospheric aerosol burden) climate forcings have been considered. Comparisons of climate reconstructions with model results indicate that all the investigated forcings are needed to simulate the surface air temperature evolution. Due to uncertainties in historical climate forcings and temperature reconstructions, the relative importance of a particular forcing in the explanation of the recorded temperature variance is largely function of the forcing time series used. Nevertheless, our results indicate that whatever the historical solar and volcanic reconstructions may be, these externally driven natural climate forcings are unable to give climate responses comparable in magnitude and time to the late-20th-century temperature warming while for earlier periods combination of solar and volcanic forcings can explain the Little Ice Age and the Medieval Warm Period. Only the greenhouse gas forcing allows the model to simulate an accelerated warming rate during the last three decades. The best guess simulation (largest similarity with the reconstruction) for the period starting 1850 AD requires however to include anthropogenic sulphate forcing as well as the impact of deforestation to constrain the magnitude of the greenhouse gas twentieth century warming to better fit the observation. On the contrary, prior to 1850 AD mid-latitude land clearance tends to reinforce the Little Ice age in our simulations.

High-dose chemotherapy with autologous stem cell transplantation as first-line therapy for primary CNS lymphoma in patients younger than 60 years: a multicenter phase II study of the GOELAMS group.

P Colombat — 2008-05-26T09:06:07-00:00

Bone marrow transplantation, Vol. 38, No. 6. (September 2006), pp. 417-420.

The optimum treatment of primary CNS lymphoma (PCNSL) is not yet determined. The objective of this study was to assess the safety and efficacy of initial methotrexate-based chemotherapy followed by high-dose chemotherapy (HDT) with autologous stem cell transplantation (ASCT) in patients with newly diagnosed PCNSL. Twenty-five patients received two courses of initial chemotherapy combining methotrexate, etoposide, carmustine and methylprednisolone, and one course of ifosfamide-cytarabine followed by peripheral stem cell collection. Seventeen responsive patients then received HDT using carmustine, etoposide, cytarabine and melphalan with autologous stem cell rescue. After ASCT for responding patients or after salvage therapy for non-responders, whole brain radiation therapy at a dose of 30 Gy was delivered. The objective response rate to the induction chemotherapy was 84%. Four of the 21 responding patients did not have ASCT because of toxicity or refusal. With a median follow-up time of 34 months, the projected event free survival rate is 46% at 4 years. Projected overall survival is 64% at 4 years. Sixteen patients are actually in continuous complete response. No evidence of late treatment-related toxicity was observed. This treatment approach appears feasible in newly diagnosed PCNSL with encouraging results.

Combined EEG and MEG recordings of visual 40 Hz responses to illusory triangles in human.

C Tallon-Baudry — 2008-05-24T17:29:20-00:00

Neuroreport, Vol. 8, No. 5. (24 March 1997), pp. 1103-1107.

EEG and MEG were simultaneously recorded to study the visual gamma-band (30-70 Hz) responses. The electrical gamma-band response phase-locked to stimulus onset can be subdivided into a central component at 39 Hz and an occipital component at 36 Hz. A new high-frequency magnetic phase-locked response recorded over the occipital lobe is described. Its topography is complex and probably reflects the activity of multiple sources. Both electrical and magnetic high-frequency responses differ in topography from the low-frequency responses in the same latency range, suggesting that at least partially distinct sources are involved. The existence of a non-phase-locked 40 Hz component around 280 ms is confirmed in EEG data but is not detectable in MEG data.

Oscillatory gamma activity in humans and its role in object representation.

C Tallon-Baudry — 2006-10-27T19:36:35-00:00

Trends Cogn Sci, Vol. 3, No. 4. (April 1999), pp. 151-162.

We experience objects as whole, complete entities irrespective of whether they are perceived by our sensory systems or are recalled from memory. However, it is also known that many of the properties of objects are encoded and processed in different areas of the brain. How then, do coherent representations emerge? One theory suggests that rhythmic synchronization of neural discharges in the gamma band (around 40 Hz) may provide the necessary spatial and temporal links that bind together the processing in different brain areas to build a coherent percept. In this article we propose that this mechanism could also be used more generally for the construction of object representations that are driven by sensory input or internal, top-down processes. The review will focus on the literature on gamma oscillatory activities in humans and will describe the different types of gamma responses and how to analyze them. Converging evidence that suggests that one particular type of gamma activity (induced gamma activity) is observed during the construction of an object representation will be discussed.

Apolipoprotein E polymorphism and Alzheimer's disease.

J Poirier — 2008-05-18T13:29:09-00:00

Lancet, Vol. 342, No. 8873. (18 September 1993), pp. 697-699.

Apolipoprotein E (apoE) is associated with Alzheimer's neurofibrillary tangles and beta-amyloid protein in senile plaques. It also appears to play an important part in the redistribution of lipids that follows deafferentation and neurodegeneration in the brain. The gene for apoE is on chromosome 19, within the genomic region previously associated with late-onset familial Alzheimer's disease (AD). We have studied apoE phenotype expression and the corresponding allele frequencies (epsilon 2, epsilon 3, epsilon 4) in 91 patients with sporadic AD and 74 controls. There was a significant association between epsilon 4 and sporadic AD (epsilon 4 frequency 0.380 in AD and 0.122 in controls, p < 0.01). Analysis of epsilon 4 in whom AD develops this tended to happen earlier in life than in those with epsilon 3 or epsilon 2. The epsilon 4/AD association was more pronounced in women. Octogenarians with AD had an epsilon 4 allele frequency that was 3 times higher than one reported, in a different study, in healthy octogenarians. ApoE may be an important susceptibility factor in the aetiopathology of sporadic AD.

From shear thickening to shear-induced jamming

Emanuel Bertrand — 2008-05-13T14:34:43-00:00

Physical Review E, Vol. 66, No. 6. (11 December 2002), 060401.

Oscillatory gamma activity in humans and its role in object representation

Catherine Tallon-Baudry — 2006-11-22T10:25:51-00:00

Trends in Cognitive Sciences, Vol. 3, No. 4. (1 April 1999), pp. 151-162.

We experience objects as whole, complete entities irrespective of whether they are perceived by our sensory systems or are recalled from memory. However, it is also known that many of the properties of objects are encoded and processed in different areas of the brain. How then, do coherent representations emerge? One theory suggests that rhythmic synchronization of neural discharges in the gamma band (around 40 Hz) may provide the necessary spatial and temporal links that bind together the processing in different brain areas to build a coherent percept. In this article we propose that this mechanism could also be used more generally for the construction of object representations that are driven by sensory input or internal, top-down processes. The review will focus on the literature on gamma oscillatory activities in humans and will describe the different types of gamma responses and how to analyze them. Converging evidence that suggests that one particular type of gamma activity (induced gamma activity) is observed during the construction of an object representation will be discussed.

Measuring the Kinetics of Biomolecular Recognition with Magnetic Colloids

Cohen Tannoudji — 2008-05-07T23:01:32-00:00

Physical Review Letters, Vol. 100, No. 10. (2008)

We introduce a general methodology based on magnetic colloids to study the recognition kinetics of tethered biomolecules. Access to the full kinetics of the reaction is provided by an explicit measure of the time evolution of the reactant densities. Binding between a single ligand and its complementary receptor is here limited by the colloidal rotational diffusion. It occurs within a binding distance that can be extracted by a reaction-diffusion theory that properly accounts for the rotational Brownian dynamics. Our reaction geometry allows us to probe a large diversity of bioadhesive molecules and tethers, thus providing a quantitative guidance for designing more efficient reactive biomimetic surfaces, as required for diagnostic, therapeutic, and tissue engineering techniques.

Neural tissue in ascidian embryos is induced by FGF9/16/20, acting via a combination of maternal GATA and Ets transcription factors.

V Bertrand — 2006-09-28T10:51:41-00:00

Cell, Vol. 115, No. 5. (26 November 2003), pp. 615-627.

In chordates, formation of neural tissue from ectodermal cells requires an induction. The molecular nature of the inducer remains controversial in vertebrates. Here, using the early neural marker Otx as an entry point, we dissected the neural induction pathway in the simple embryos of Ciona intestinalis. We first isolated the regulatory element driving Otx expression in the prospective neural tissue, showed that this element directly responds to FGF signaling and that FGF9/16/20 acts as an endogenous neural inducer. Binding site analysis and gene loss of function established that FGF9/16/20 induces neural tissue in the ectoderm via a synergy between two maternal response factors. Ets1/2 mediates general FGF responsiveness, while the restricted activity of GATAa targets the neural program to the ectoderm. Thus, our study identifies an endogenous FGF neural inducer and its early downstream gene cascade. It also reveals a role for GATA factors in FGF signaling.

Object Representation and Gamma Oscillations

Bertrand — 2008-05-05T06:45:04-00:00

this paper, we will present the different types of 40-Hz responses reported in the literature, and show some evidence for a role of induced gamma oscillations in sensory information processing (both visual and auditory) and memory rehearsal, in other words, in brain processes requiring the activation of a coherent object representations. The neural substrate of those gamma oscillations observed on the scalp will also be discussed

Nature, origin, transport and deposition of andosol parent material in south-central Chile (36-42°S)

Sébastien Bertrand — 2008-05-02T19:52:44-00:00

CATENA, Vol. 73, No. 1. (15 March 2008), pp. 10-22.

The andosols of south-central Chile (36-42°S) are developed on yellow-brown loams that cover the region with a thickness of several meters. In the literature, several hypotheses concerning the nature, origin, mode of transport and deposition of the andosol parent material have been advanced but no general agreement has been found. In this paper, we test these hypotheses by analyzing new representative outcrops located around Icalma (38°50'S) and Puyehue (40°40'S) lakes by a pluri-methodological approach. Our data demonstrate that the andosol parent material has the typical mineralogical and geochemical signature of the regional volcanism and that these deposits are post-glacial in age. The grain size of the deposits and the morphology of the coarse grains evidence that most of these particles haven't been re-transported by wind but are direct volcanic ash falls deposited throughout the Late Glacial and Holocene. Because of the prevailing westerly winds, most of these volcanic ashes have been transported to the East. Following the deposition of the volcanic particles, weathering and pedogenetic processes have transformed part of the volcanic glasses and plagioclases into allophane and have wiped out the original layering. This work demonstrates that most of the andosols that occur in the Andes and in the eastern part of the Intermediate Depression of south-central Chile are developed on volcanic ashes directly deposited by successive volcanic eruptions throughout the Late Glacial and Holocene.

Coexistence of Liquid and Solid Phases in Flowing Soft-Glassy Materials

P Coussot — 2008-03-31T13:15:36-00:00

Physical Review Letters, Vol. 88, No. 21. (May 2002), 218301.

Magnetic-resonance-imaging rheometrical experiments show that concentrated suspensions or emulsions cannot flow steadily at a uniform rate smaller than a critical value ( γ̇ c ). As a result; a “liquid” region (sheared rapidly; i.e.; at a rate larger than γ̇ c ) and a “solid” region (static) coexist. The behavior of the fluid in the liquid region follows a simple power-law model; while the extent of the solid region increases with the degree of jamming of the material.

Reconstruction of the Holocene seismotectonic activity of the Southern Andes from seismites recorded in Lago Icalma, Chile, 39°S

Sébastien Bertrand — 2008-04-24T13:34:27-00:00

Palaeogeography, Palaeoclimatology, Palaeoecology, Vol. 259, No. 2-3. (24 March 2008), pp. 301-322.

South-central Chile is one of the most geodynamically active areas in the world, characterized by frequent volcanic eruptions and numerous earthquakes, which are both recorded in lake sediments. In Lago Icalma (39°S), long piston and short gravity coring, as well as 3.5 kHz high-resolution seismic profiling, have been carried out in order to study the Holocene sedimentary infill of the lake, with a special focus on earthquake-triggered deposits. Macroscopic description of sediment cores and detailed grain-size analyses allow us to identify four types of seismically-induced deposits, or "seismites": slump deposits, chaotic deposits, turbidites s.s. and homogenites. Homogenites are characterized by the occurrence of three distinct units on grain-size profiles (i.e., a coarse base, a thick homogeneous unit topped by a thin layer of very fine sediment) and by the typical distribution of the grain-size parameters in a skewness-sorting diagram, while turbidites s.s. are characterized by a continuous fining-upward trend. Radiocarbon, 210Pb dating, and tephrochronology allow us to demonstrate that the regional seismotectonic activity was probably very high between 2200 and 3000 cal years BP as well as between 7000 and 8000 cal years BP and that none of the historically documented earthquakes has triggered a seismite in Lago Icalma. The most recent seismite recognized in the sediments of Lago Icalma is a slump deposit dated at 1100 ± 100 AD, i.e., older than the period covered by historical records. The remarkable record of seismites between 2200 and 3000 cal years BP is probably influenced by a major eruption of Sollipulli volcano at 3000 cal years BP, which has rejuvenated the stock of terrigenous particles available for erosion, by depositing a thick layer of pumices all over the watershed of Lago Icalma and by clearing the vegetation covering the volcanic ash soils. This paper demonstrates that the record of seismically-triggered deposits in lake sediments is not only controlled by the intensity of the triggering earthquake and the occurrence of unstable sediment along the lake slopes but also by the presence of particles available for erosion/remobilisation in the watershed.

Irreversible Shear-Activated Aggregation in Non-Brownian Suspensions

J Guery — 2008-04-23T18:01:46-00:00

Physical Review Letters, Vol. 96, No. 19. (2006)

We have studied the effect of shear on the stability of suspensions made of non-Brownian solid particles. We demonstrate the existence of an irreversible transition where the solid particles aggregate at remarkably low volume fractions (0.1). This shear-induced aggregation is dramatic and exhibits a very sudden change in the viscosity, which increases sharply after a shear-dependent induction time. We show that this induction time is related exponentially to the shear rate, reflecting the importance of the hydrodynamic forces in reducing the repulsive energy barrier that prevents the particles from aggregating.

Adaptive finite element simulations of fluid flow in twin-screw extruders

F Bertrand — 2008-04-21T09:42:19-00:00

Computers & Chemical Engineering, Vol. 27, No. 4. (15 April 2003), pp. 491-500.

The objective of this work1 is to present a new strategy for the transient simulation of fluid flow in geometries involving moving parts and small gaps. It is based upon a fictitious domain method and a mesh refinement technique that relies upon one single reference mesh. With this technique, at each time iteration, the reference mesh may be adapted locally according for instance to the position of the gaps in the computational domain. The method will be discussed in detail and applied to the two-dimensional (2D) simulation of fluid flow in twin-screw extruders where one of the key issues is the ability to predict accurately the shear rates in the gaps formed by the rotating screws.

Affirmative Action in Education: Evidence From Engineering College Admissions in India

Marianne Bertrand — 2008-04-11T16:38:47-00:00

National Bureau of Economic Research Working Paper Series (April 2008), 13926.

Author contact info: Marianne Bertrand Graduate School of Business University of Chicago 5807 South Woodlawn Avenue Chicago, IL 60637 Tel: 773/834-5943 Fax: 773/702-0458 E-Mail: marianne.bertrand@gsb.uchicago.edu Rema Hanna Wagner Graduate School of Public Service New York University 295 Lafayette Street, 2Fl New York, NY 10012 Tel: 212-998-7443 Fax: 212-995-4162 E-Mail: rnh4@nyu.edu Sendhil Mullainathan Department of Economics Littauer 208 Harvard University Cambridge, MA 02138 Tel: 617/496-2720 Fax: 617/495-7730 E-Mail: mullain@fas.harvard.edu Many countries mandate affirmative action in university admissions for traditionally disadvantaged groups. Little is known about either the efficacy or costs of these programs. This paper examines affirmative action in engineering colleges in India for "lower-caste" groups. We find that it successfully targets the financially disadvantaged: the marginal upper-caste applicant comes from a more advantaged background than the marginal lower-caste applicant who displaces him. Despite much lower entrance exam scores, the marginal lower-caste entrant does benefit: we find a strong, positive economic return to admission. These findings contradict common arguments against affirmative action: that it is only relevant for richer lower-caste members, or that those who are admitted are too unprepared to benefit from the education. However, these benefits come at a cost. Our point estimates suggest that the marginal upper-caste entrant enjoys nearly twice the earnings level gain as the marginal lower-caste entrant. This finding illustrates the program's redistributive nature: it benefits the poor, but costs resources in absolute terms. One reason for this lower level gain is that a smaller fraction of lower-caste admits end up employed in engineering or advanced technical jobs. Finally, we find no evidence that the marginal upper-caste applicant who is rejected due to the policy ends up with more negative attitudes towards lower castes or towards affirmative action programs. On the other hand, there is some weak evidence that the marginal lower-caste admits become stronger supporters of affirmative action programs.

Interplay between neuromodulator-induced switching of short-term plasticity at sensorimotor synapses in the neonatal rat spinal cord

Barriere — 2008-04-03T18:15:18-00:00

The Journal of Physiology, Vol. 586, No. 7. (April 2008), pp. 1903-1920.

Time-frequency digital filtering based on an invertible wavelet transform: an application to evoked potentials.

O Bertrand — 2008-04-01T13:24:57-00:00

IEEE Trans Biomed Eng, Vol. 41, No. 1. (January 1994), pp. 77-88.

This paper presents a method to analyze and filter digital signals of finite duration by means of a time-frequency representation. This is done by defining a purely invertible discrete transform, representing a signal either in the time or in the time-frequency domain, as simply as possible with the conventional discrete Fourier transform between the time and the frequency domains. The wavelet concept has been used to build this transform. To get a correct invertibility of this procedure, we have proposed orthogonal and periodic basic discrete wavelets. The properties of such a transform are described, and examples on brain-evoked potential signals are given to illustrate the time-frequency filtering possibilities.

Long-term results of related myeloablative stem-cell transplantation to cure sickle cell disease

Francoise Bernaudin — 2008-03-29T14:01:14-00:00

Blood, Vol. 110, No. 7. (1 October 2007), pp. 2749-2756.

Allogeneic hematopoietic stem-cell transplantation (HSCT) is the only curative treatment for sickle cell disease (SCD); nevertheless, its use has been limited by the risk of transplantation-related mortality (TRM). Between November 1988 and December 2004, 87 consecutive patients with severe SCD ranging from 2 to 22 years of age received transplants in France. Cerebral vasculopathy was the principal indication for transplantation (55 patients). All the patients received grafts from a sibling donor after a myeloablative conditioning regimen (CR). The only change in the CR during the study period was the introduction of antithymocyte globulin (ATG) in March 1992. The rejection rate was 22.6% before the use of ATG but 3% thereafter. With a median follow-up of 6 years (range, 2.0 to 17.9 years), the overall and event-free survival (EFS) rates were 93.1% and 86.1%, respectively. Graft versus host disease (GVHD) was the main cause of TRM. Importantly, cord blood transplant recipients did not develop GVHD. No new ischemic lesions were detected after engraftment, and cerebral velocities were significantly reduced. The outcome improved significantly with time: the EFS rate among the 44 patients receiving transplants after January 2000 was 95.3%. These results indicate that HLA-identical sibling HSCT after myeloablative conditioning with ATG should be considered as a standard of care for SCD children who are at high risk for stroke. 10.1182/blood-2007-03-079665

Ligands playing musical chairs with G-quadruplex DNA: A rapid and simple displacement assay for identifying selective G-quadruplex binders.

D Monchaud — 2008-03-18T22:52:29-00:00

Biochimie (4 March 2008)

We report here the details of G4-FID (G-quadruplex fluorescent intercalator displacement), a simple method aiming at evaluating quadruplex-DNA binding affinity and quadruplex- over duplex-DNA selectivity of putative ligands. This assay is based on the loss of fluorescence upon displacement of thiazole orange from quadruplex- and duplex-DNA matrices. The original protocol was tested using various quadruplex- and duplex-DNA targets, and with a wide panel of G-quadruplex ligands belonging to different families (i.e. from quinacridines to metallo-organic ligands) likely to display various binding modes. The reliability of the assay is further supported by comparisons with FRET-melting and ESI-MS assays.

About the relationship between eyebrow movements and F0 variations

C Cav\a'e — 2008-03-07T13:31:09-00:00

Proceedings ICSLP 96 (1996), pp. 2175-2178.

Speech production is always accompanied by facial and gestural activity. The present study is part of a broader research project on how head movements and facial expressions are related to voice variations in different speech situations. Ten normal subjects were recorded while reading aloud, answering yes/no questions, and dialoguing with an interviewer. Rapid rising-falling eyebrow movements produced by the subjects as they spoke were associated with Fo rises in only 71% of the cases. This...

Glutaraldehyde: behavior in aqueous solution, reaction with proteins, and application to enzyme crosslinking.

I Migneault — 2008-03-05T13:02:03-00:00

Biotechniques, Vol. 37, No. 5. (November 2004)

Glutaraldehyde possesses unique characteristics that render it one of the most effective protein crosslinking reagents. It can be present in at least 13 different forms depending on solution conditions such as pH, concentration, temperature, etc. Substantial literature is found concerning the use of glutaraldehyde for protein immobilization, yet there is no agreement about the main reactive species that participates in the crosslinking process because monomeric and polymeric forms are in equilibrium. Glutaraldehyde may react with proteins by several means such as aldol condensation or Michael-type addition, and we show here 8 different reactions for various aqueous forms of this reagent. As a result of these discrepancies and the unique characteristics of each enzyme, crosslinking procedures using glutaraldehyde are largely developed through empirical observation. The choice of the enzyme-glutaraldehyde ratio, as well as their final concentration, is critical because insolubilization of the enzyme must result in minimal distortion of its structure in order to retain catalytic activity. The purpose of this paper is to give an overview of glutaraldehyde as a crosslinking reagent by describing its structure and chemical properties in aqueous solution in an attempt to explain its high reactivity toward proteins, particularly as applied to the production of insoluble enzymes.

Terlipressin-ephedrine versus ephedrine to treat hypotension at the induction of anesthesia in patients chronically treated with angiotensin converting-enzyme inhibitors: a prospective, randomized, double-blinded, crossover study.

K Meersschaert — 2008-03-05T06:39:22-00:00

Anesth Analg, Vol. 94, No. 4. (April 2002)

In patients chronically treated with angiotensin converting-enzyme inhibitors (ACEI), typically selected doses of ephedrine do not always restore arterial blood pressure when anesthesia-induced hypotension occurs. We postulated that the administration of terlipressin, an agonist of the vasopressin system, with ephedrine more effectively restores pressure in this setting than the administration of ephedrine alone. This prospective, randomized, cross-over, double-blinded study compared terlipressin combined with ephedrine (n = 19) with ephedrine alone (n = 21) in treating hypotension at the induction of anesthesia in 40 ACEI-treated patients undergoing hypotension (mean arterial blood pressure [MAP] <65 mm Hg or <30% of baseline value) after standardized anesthetic protocol (target-controlled IV anesthesia with propofol). Data are mean +/- SD. Patient characteristics, MAP, and heart rate before and after the induction of anesthesia during hypotensive episodes were not significantly different between the two groups. After the first bolus, MAP was significantly greater in the Terlipressin-Ephedrine group (72 +/- 12 mm Hg versus 65 +/- 8 mm Hg, P < 0.05). The occurrence of a second hypotensive episode (5% versus 71%, P < 0.001), the duration (2 +/- 1 min versus 3 +/- 1 min, P < 0.01) of hypotensive episodes, and the median dose of ephedrine (3 versus 6 mg, P < 0.05) were significantly less in the Terlipressin-Ephedrine group. In conclusion, terlipressin combined with ephedrine is more effective than ephedrine alone for treating anesthesia-induced hypotension in ACEI-treated patients. We conclude that this patient population with a partially blocked endogenous response to hypotension may be good candidates for successful use of a vasopressin analog to counteract intraoperative refractory hypotension. IMPLICATIONS: Vascular surgical patients chronically treated with drugs that inhibit the functioning of the renin-angiotensin system may experience hypotension unresponsive to conventional therapy. This double-blinded, cross-over study demonstrated that in these patients the use of a vasopressin analog, terlipressin given with ephedrine, was effective in reversing intraoperative systemic hypotension refractory to ephedrine.

Terlipressin versus norepinephrine to correct refractory arterial hypotension after general anesthesia in patients chronically treated with renin-angiotensin system inhibitors.

G Boccara — 2008-03-05T06:38:27-00:00

Anesthesiology, Vol. 98, No. 6. (June 2003), pp. 1338-1344.

BACKGROUND: Terlipressin, a precursor that is metabolized to lysine-vasopressin, has been proposed as a drug for treatment of intraoperative arterial hypotension refractory to ephedrine in patients who have received long-term treatment with renin-angiotensin system inhibitors. The authors compared the effectiveness of terlipressin and norepinephrine to correct hypotension in these patients. METHODS: Among 42 patients scheduled for elective carotid endarterectomy, 20 had arterial hypotension following general anesthesia that was refractory to ephedrine. These patients were the basis of the study. After randomization, they received either 1 mg intravenous terlipressin (n = 10) or norepinephrine infusion (n = 10). Beat-by-beat recordings of systolic arterial blood pressure and heart rate were stored on a computer. The intraoperative maximum and minimum values of blood pressure and heart rate, and the time spent with systolic arterial blood pressure below 90 mmHg and above 160 mmHg, were used as indices of hemodynamic stability. Data are expressed as median (95% confidence interval). RESULTS: Terlipressin and norepinephrine corrected arterial hypotension in all cases. However, time spent with systolic arterial blood pressure below 90 mmHg was less in the terlipressin group (0 s [0-120 s] vs. 510 s [120-1011 s]; P < 0.001). Nonresponse to treatment (defined as three boluses of terlipressin or three changes in norepinephrine infusion) occurred in zero and eight cases (P < 0.05), respectively. CONCLUSIONS: In patients who received long-term treatment with renin-angiotensin system inhibitors, intraoperative refractory arterial hypotension was corrected with both terlipressin and norepinephrine. However, terlipressin was more rapidly effective for maintaining normal systolic arterial blood pressure during general anesthesia.

The creation of a brain atlas for image guided neurosurgery using serial histological data

Mallar Chakravarty — 2008-03-04T16:51:42-00:00

NeuroImage, Vol. 30, No. 2. (1 April 2006), pp. 359-376.

Digital and print brain atlases have been used with success to help in the planning of neurosurgical interventions. In this paper, a technique presented for the creation of a brain atlas of the basal ganglia and the thalamus derived from serial histological data. Photographs of coronal histological sections were digitized and anatomical structures were manually segmented. A slice-to-slice nonlinear registration technique was used to correct for spatial distortions introduced into the histological data set at the time of acquisition. Since the histological data were acquired without any anatomical reference (e.g., block-face imaging, post-mortem MRI), this registration technique was optimized to use an error metric which calculates a nonlinear transformation minimizing the mean distance between the segmented contours between adjacent pairs of slices in the data set. A voxel-by-voxel intensity correction field was also estimated for each slice to correct for lighting and staining inhomogeneity. The reconstructed three-dimensional (3D) histological volume can be viewed in transverse and sagittal directions in addition to the original coronal. Nonlinear transformations used to correct for spatial distortions of the histological data were applied to the segmented structure contours. These contours were then tessellated to create three-dimensional geometric objects representing the different anatomic regions in register with the histological volumes. This yields two alternate representations (one histological and one geometric) of the atlas. To register the atlas to a standard reference MR volume created from the average of 27 T1-weighted MR volumes, a pseudo-MRI was created by setting the intensity of each anatomical region defined in the geometric atlas to match the intensity of the corresponding region of the reference MR volume. This allowed the estimation of a 3D nonlinear transformation using a correlation based registration scheme to fit the atlas to the reference MRI. The result of this procedure is a contiguous 3D histological volume, a set of 3D objects defining the basal ganglia and thalamus, both of which are registered to a standard MRI data set, for use for neurosurgical planning.

Diagnostic efficiency, embryonic development and clinical outcome after the biopsy of one or two blastomeres for preimplantation genetic diagnosis

Veerle Goossens — 2008-02-28T16:41:44-00:00

Hum. Reprod., Vol. 23, No. 3. (1 March 2008), pp. 481-492.

BACKGROUNDPreimplantation genetic diagnosis or screening (PGD, PGS) involves embryo biopsy on Day 3. Opting for one- or two-cell biopsy is a balance between the lowest risk for misdiagnosis on the one hand and the highest chance for a pregnancy on the other hand. METHODSA prospective controlled trial was designed and 592 ICSI cycles were randomly assigned to the one-cell (group I) or the two-cell group (group II). Primary outcomes were diagnostic efficiency and embryonic development to delivery with live birth (analysed by cycle). The false-positive rate for the PCR cycles is presented as a secondary outcome (analysed by embryo). RESULTSA strong significant correlation was observed between embryonic developmental stage on Day 3 and post-biopsy in vitro development on Day 5 (P < 0.0001). The influence of the intervention on Day 3 was less significant (P = 0.007): the biopsy of one cell is less invasive than the biopsy of two cells. PCR diagnostic efficiency was 88.6% in group I and 96.4% in group II (P = 0.008). For the fluorescence in situ hybridization (FISH) PGD cycles no significant difference in efficiency was obtained (98.2 and 97.5% in group I and II, respectively). Similar delivery rates with live birth per started cycle were obtained [58/287 or 20.2% in group I versus 52/303 or 17.2% in group II, P = 0.358; the absolute risk reduction = 3.05%; 95% confidence interval (CI): 3.24, 9.34]. Post-PGD PCR reanalysis showed six false positives in 97 embryos (6.2%) in group II and none in group I (91 embryos reanalysed). No false negatives were found. CONCLUSIONSWhile removal of two blastomeres decreases the likelihood of blastocyst formation, compared with removal of one blastomere, Day 3 in vitro developmental stage is a stronger predictor for Day 5 developmental potential than the removal of one or two cells. The biopsy of only one cell significantly lowers the efficiency of a PCR-based diagnosis, whereas the efficiency of the FISH PGD procedure remains similar whether one or two cells are removed. Delivery rates with live birth per started cycle were not significantly different. 10.1093/humrep/dem327

Silence Is Golden: Transient Neural Deactivation in the Prefrontal Cortex during Attentive Reading.

Jp Lachaux — 2007-07-27T22:08:27-00:00

Cereb Cortex (7 July 2007)

It is becoming increasingly clear that attention-demanding tasks engage not only activation of specific cortical regions but also deactivation of other regions that could interfere with the task at hand. At the same time, electrophysiological studies in animals and humans have found that the participation of cortical regions to cognitive processes translates into local synchronization of rhythmic neural activity at frequencies above 40 Hz (so-called gamma-band synchronization). Such synchronization is seen as a potential facilitator of neural communication and synaptic plasticity. We found evidence that cognitive processes can also involve the disruption of gamma-band activity in high-order brain regions. Intracerebral electroencephalograms were recorded in 3 epileptic patients during 2 reading tasks. Visual presentation of words induced a strong deactivation in a broad (20-150 Hz) frequency range in the left ventral lateral prefrontal cortex, in parallel with gamma-band activations within the reading network, including Broca's area. The observed energy decrease in neural signals was reproducible across patients. It peaked around 500 ms after stimulus onset and appeared subject to attention-modulated amplification. Our results suggest that cognition might be mediated by a coordinated interaction between regional gamma-band synchronizations and desynchronizations, possibly reflecting enhanced versus reduced local neural communication.

Inhibition of Translational Initiation by Let-7 MicroRNA in Human Cells

Ramesh Pillai — 2005-09-06T18:51:32-00:00

Science, Vol. 309, No. 5740. (02 September 2005), pp. 1573-1576.

MicroRNAs (miRNAs) are [~]21-nucleotide-long RNA molecules regulating gene expression in multicellular eukaryotes. In metazoa, miRNAs act by imperfectly base-pairing with the 3' untranslated region of target messenger RNAs (mRNAs) and repressing protein accumulation by an unknown mechanism. We demonstrate that endogenous let-7 microribonucleoproteins (miRNPs) or the tethering of Argonaute (Ago) proteins to reporter mRNAs in human cells inhibit translation initiation. M7G-cap-independent translation is not subject to repression, suggesting that miRNPs interfere with recognition of the cap. Repressed mRNAs, Ago proteins, and miRNAs were all found to accumulate in processing bodies. We propose that localization of mRNAs to these structures is a consequence of translational repression.

Climate variability of southern Chile since the Last Glacial Maximum: a continuous sedimentological record from Lago Puyehue (40°S)

Sébastien Bertrand — 2008-02-22T15:16:47-00:00

Journal of Paleolimnology, Vol. 39, No. 2. (16 February 2008), pp. 179-195.

Abstract This paper presents a multi-proxy climate record of an 11 m long core collected in Lago Puyehue (southern Chile, 40°S) and extending back to 18,000 cal yr BP. The multi-proxy analyses include sedimentology, mineralogy, grain size, geochemistry, loss-on-ignition, magnetic susceptibility and radiocarbon dating. Results demonstrate that sediment grain size is positively correlated with the biogenic sediment content and can be used as a proxy for lake paleoproductivity. On the other hand, the magnetic susceptibility signal is correlated with the aluminium and titanium concentrations and can be used as a proxy for the terrigenous supply. Temporal variations of sediment composition evidence that, since the Last Glacial Maximum, the Chilean Lake District was characterized by three abrupt climate changes superimposed on a long-term climate evolution. These rapid climate changes are: (1) an abrupt warming at the end of the Last Glacial Maximum at 17,300 cal yr BP; (2) a 13,100–12,300 cal yr BP cold event, ending rapidly and interpreted as the local counterpart of the Younger Dryas cold period, and (3) a 3,400–2,900 cal yr BP climatic instability synchronous with a period of low solar activity. The timing of the 13,100–12,300 cold event is compared with similar records in both hemispheres and demonstrates that this southern hemisphere climate change precedes the northern hemisphere Younger Dryas cold period by 500 to 1,000 years.

Medial temporal lobe activations during associative memory encoding for arbitrary and semantically related object pairs

Amelie Achim — 2008-02-21T23:33:24-00:00

Brain Research, Vol. 1161 (3 August 2007), pp. 46-55.

Previous positron emission tomography (PET) studies have shown greater medial temporal lobe activation (MTL) for associative memory encoding relative to deep item-oriented encoding. Greater MTL activation has also been reported for associative novelty detection. Although it has been suggested that these patterns of MTL activation could reflect the creation of novel associations into memory, it is unclear whether associative encoding and associative novelty detection rely on the same MTL substructures. In this study, we used event-related functional magnetic resonance imaging (er-fMRI) to reproduce previous reports of greater hippocampal activation for associative encoding using both arbitrary and semantically related object pairs. This paradigm allowed us to assess whether the requirement for associative processing at encoding interacts with associative novelty. Contrasting the pattern of activation for associative versus item-oriented encoding revealed greater right hippocampal activation as well as parahippocampal activation bilaterally, reproducing the findings from previous PET experiments. The orthogonal contrast between arbitrary and related pairs revealed greater activation in the left parahippocampal region, but no significant interaction between the type of encoding (associative or item oriented) and the type of pairs (arbitrary or semantically related) was observed in the medial temporal lobe (MTL). These results suggest that both associative processing and associative novelty detection can activate the MTL. Most importantly, this study suggests that associative processing can activate the MTL regardless of the pre-existence of an association between the items of a pair.

Artemis, a novel DNA double-strand break repair/V(D)J recombination protein, is mutated in human severe combined immune deficiency.

D Moshous — 2008-02-04T06:14:48-00:00

Cell, Vol. 105, No. 2. (20 April 2001), pp. 177-186.

The V(D)J recombination process insures the somatic diversification of immunoglobulin and antigen T cell receptor encoding genes. This reaction is initiated by a DNA double-strand break (dsb), which is resolved by the ubiquitously expressed DNA repair machinery. Human T-B-severe combined immunodeficiency associated with increased cellular radiosensitivity (RS-SCID) is characterized by a defect in the V(D)J recombination leading to an early arrest of both B and T cell maturation. We previously mapped the disease-related locus to the short arm of chromosome 10. We herein describe the cloning of the gene encoding a novel protein involved in V(D)J recombination/DNA repair, Artemis, whose mutations cause human RS-SCID. Protein sequence analysis strongly suggests that Artemis belongs to the metallo-beta-lactamase superfamily.

Are Emily and Greg More Employable than Lakisha and Jamal? A Field Experiment on Labor Market Discrimination

Marianne Bertrand — 2008-01-29T04:35:09-00:00

National Bureau of Economic Research Working Paper Series (July 2003), 9873.

Author contact info: Marianne Bertrand Graduate School of Business University of Chicago 5807 South Woodlawn Avenue Chicago, IL 60637 Tel: 773/834-5943 Fax: 773/702-0458 E-Mail: marianne.bertrand@gsb.uchicago.edu Sendhil Mullainathan Department of Economics Littauer 208 Harvard University Cambridge, MA 02138 Tel: 617/496-2720 Fax: 617/495-7730 E-Mail: mullain@fas.harvard.edu We perform a field experiment to measure racial discrimination in the labor market. We respond with fictitious resumes to help-wanted ads in Boston and Chicago newspapers. To manipulate perception of race, each resume is assigned either a very African American sounding name or a very White sounding name. The results show significant discrimination against African-American names: White names receive 50 percent more callbacks for interviews. We also find that race affects the benefits of a better resume. For White names, a higher quality resume elicits 30 percent more callbacks whereas for African Americans, it elicits a far smaller increase. Applicants living in better neighborhoods receive more callbacks but, interestingly, this effect does not differ by race. The amount of discrimination is uniform across occupations and industries. Federal contractors and employers who list Equal Opportunity Employer' in their ad discriminate as much as other employers. We find little evidence that our results are driven by employers inferring something other than race, such as social class, from the names. These results suggest that racial discrimination is still a prominent feature of the labor market.